Recently, improving automobile fuel efficiency has become a matter of great urgency, considering the depletion of our oil resources, global warming, and the like. To improve automotive performance and meet with consumer demand, various measures have been taken to seriously improve soundproofing both on the inside and outside of a car, and many kinds of sound absorbing material have been provided for this purpose. Most of said sound absorbing materials are laminated materials, wherein a sound absorbing surface material is laminated onto a base sheet, after which the resulting green laminated material is molded into a predetermined shape.
Generally, a porous sheet such as a fiber sheet like a nonwoven fabric, a glass wool, a foamed polyurethane sheet or the like has been used as a surface material. Further, it is known that the ventilation resistance of the surface material must be adjusted to be in the range of between about 0.6 and 20.0 kPa·s/m, to ensure the maximum performance of the sound absorption and insulation over a wide frequency range.
For instance, Patent Literature 1 discloses a sound absorbing felt made of a single felt layer. Patent Literature 2 discloses a car interior made of a fiber web containing a synthetic resin binder. Further Patent Literature 3 discloses a car insulator made of a laminated material consisting of a sound absorbing fiber layer and foamed surface material.    Patent Literature 1: Tokkai 2005-195989    Patent Literature 2: Tokkai 2004-325973    Patent Literature 3: Tokkai 2003-081028